Ra's al Ghul is the immortal leader of the League of Assassins.
In "Fall", a flashback reveals that he encountered MI6 Agents Alfred Pennyworth and Edogawa Yamashiro (the father of Katana) in the past with Edogawa forced to betray Alfred to Ra's in their last encounter under threat of his family. Ra's ordered Edogawa to use the Soultaker Sword on Alfred, but Alfred fought back, causing the powers of the sword to activate, leading to Edogawa's death. In the present day, he is revived by Lady Shiva and is ready to use the Ion Cortex to drain all of Gotham City's electricity leaving it in darkness. Batman and Katana arrive to stop him. Ra's al Ghul fights hand-to-hand against Batman where he defeats Batman considering him a "worthy opponent." Ra's al Ghul nearly kills Batman before Alfred arrives and interferes. Katana and Alfred barely escape from the League of Assassins with Ra's al Ghul commenting on how Alfred killed Edogawa. Ra's al Ghul activates the Ion Cortex plunging all of Gotham City into darkness.
In "Darkness", Ra's al Ghul directly threatens Gotham's citizens by making an example of it to the rest of the world by taking it over and "cleansing" it from the evils of technology, and even has the unnamed police commissioner killed to make his point. In addition, he has Alfred and Katana captured when they try to break into his lair. He also causes a breakout at Blackgate Penitentiary at the end of the episode.
In "Reckoning", Ra's al Ghul recruits Professor Pyg, Mr. Toad, Magpie, Tobias Whale, and Phosphorus Rex as well as League of Assassins operative Cypher to kill Batman (who had escaped with the help of an imprisoned Silver Monkey) in exchange of a small piece of the city. Ra's al Ghul also manipulates Katana into killing Alfred to avenge the death of her father. She refuses nearly having Ra's al Ghul kill them all only for Tobias to arrive with a captured Batman. Batman breaks free and stalls Ra's al Ghul in combat while Barbara Gordon hacks into the Ion Cortex, disabling it from the League of Assassins' control and bringing electricity back into the city. Batman ultimately defeats Ra's al Ghul by using a reverse chant to release all of the souls in the Soultaker Sword (particularly all of Ra's al Ghul enemies throughout the centuries). The angry spirits drag Ra's al Ghul into a bottomless pit, presumably to his death.